Ecosystem: Patterns, Components; Productivity and Decomposition

Introduction

The ecosystem is defined as a self-sustaining and self-regulatory structural and functional unit of the biosphere comprising of a community of living beings and a physical environment both interacting and exchanging materials among them. A.G Tansley firstly coined the term ecosystem in 1935. 

Types of Ecosystem

There are two types of ecosystem: 

• Terrestrial ecosystem: it is a land-based ecosystem

• Forest ecosystem: it comprises various plants, animals, and microorganisms that live in coordination with abiotic factors. The major function of the forest ecosystem is to maintain the temperature of the earth

• Grassland ecosystem: this ecosystem is dominated mostly by grasses and herbs, e.g. savannah grassland

• Tundra ecosystem: this ecosystem is found in cold areas where rainfall is scarce, and no trees are present. Most of the time in a year these are covered with snow

• Dessert ecosystem: this type of ecosystem shows warmer days and colder nights, with little rainfall

• Aquatic Ecosystem: these ecosystems are found in the body of water. These are further grouped into:

• Freshwater Ecosystem: this type of aquatic ecosystem are devoid of salt content, e.g. streams, wetlands, rivers, lakes, and ponds 

• Marine Ecosystem: this ecosystem contains salt and shows greater biodiversity than freshwater ecosystems, e.g. oceans and seas

Components of Ecosystem

Every ecosystem has both structural and functional components. Ecosystem refers to an open system that receives input in form of solar energy, and the flow of this energy is unidirectional from producers to consumers. The ecosystem is divided into two distinct components:

Biotic Component: this component of the ecosystem includes all the living members of the ecosystem such as:

• Producers: these are also known as autotrophs. Producers help in the fixation of light energy, use of simple inorganic substances, and synthesis of complex organic substances. As the members of autotrophs can convert light energy to chemical energy these are referred to as producers. E.g algae, bryophytes and vascular plants

• Consumers: they are also known as heterotrophs. Their main function is the intake, rearrangement, and utilisation of complex inorganic materials. Members involved are known as consumers as they can consume organic food

Consumers are further divided into

• Primary consumers: they generally refer to herbivores. They rely on plants for their food

• Secondary consumers: the members of this group are dependent on primary consumers, they can either be carnivores or omnivores

• Tertiary consumers: they depend on secondary consumers for food. They are omnivores

• Quaternary consumers: they depend on tertiary consumers. They are present only in some food chains. Quaternary consumers are generally present at the top of the food chain, having no natural predators

• Decomposers: since they feed on dead bodies of organisms and organic wastes of living organisms, they come under saprotrophs. The members of this group secret digestive enzymes to digest the organic matter. As they can remove the dead bodies of organisms they are known as reducers. Because of their small size, they are also known as micro consumers. E.g. bacteria, fungi

• Abiotic Components: it includes all the non-living components such as light, wind, soil, temperature, and water

Patterns of Ecosystem

The interaction of biotic components with abiotic components leads to a physical pattern that is the characteristics for each type of ecosystem such as: 

• Species composition: it refers to the identification and enumeration of plants and animals species of the ecosystem. Based the geography, topography, and climate species composition varies greatly. Areas with maximum species diversity occurs in coral reefs, and tropical rainforest

• Stratification: refers to the vertical distribution of various species occupying different levels, e.g. canopy trees and under-story trees at the top

Productivity

It refers to the rate of biomass production, per unit area over some time by plants. The rate at which sunlight gets accumulated by producers for the synthesis of organic compounds, which is expressed in terms of Kcal per metre square per year. It includes the following types: 

Primary productivity: it refers to the amount of biomass produced per unit area over some time by plants during photosynthesis. It is further classified into two types:

• Gross primary productivity (GPP): refers to the rate of production of organic matter by green plants per unit area in unit time during photosynthesis

• Net primary productivity (NPP): a definite amount of GPP is utilised by plants in respiration. After respiration, a considerable amount of energy is left which is stored as organic matter in producers in unit time and area is NPP. NPP is the only available biomass for consumption to heterotrophs

NPP = GPP – R

The annual NPP of the whole biosphere is about 170 billion tons of organic matter, of this about 70 percent is pre-occupied by the surface, about 55 billion tons indicates the productivity of oceans. Rest about 115 billion tons is made available for land productivity.

• Secondary productivity: it is the rate of assimilation of food energy by consumers, thus it is the energy available at consumers’ level for transfer to the next trophic level

Decomposition

It is the physical and chemical breakdown of complex organic matter(i.e. detritus) into inorganic substances like carbon dioxide, water, and nutrients, this process is known as decomposition. E.g. of best decomposer is earthworm that helps in the breakdown of complex organic matter as well as in the loosening of the soil. The detritus comprises the remains of dead plants such as leaves, barks, flowers, and dead remains of animals, including their fecal matter, all of these form the raw material for decomposition.  

Decomposition completely disposes of the whole detritus. The biogeochemical are recycled by decomposition and create space for newer generations of organisms. There are two types of detritus: above-ground detritus includes (leaf, dried plants parts, remains of animals, etc.) and below-ground detritus includes (mainly dead roots, also remains of underground dead animals). 

Decomposition is controlled by the chemical composition of detritus and some climatic factors. The rate of decomposition is slower if it is rich in lignin and chitin, it is quicker if it contains nitrogen and water-soluble substances like sugars. There are about five processes involved in decomposition these includes:

• Fragmentation: is the process in which detritus is broken down into smaller particles due to the action of detritivores such as (termites, earthworms), detritus is ground completely when it passes through the digestive tracts of animals. This causes an increase in the surface area of detritus particles

• Catabolism: decomposers like bacteria and fungi excrete digestive enzymes over detritus that change the insoluble complex organic substances into simple, organic substances and inorganic compounds. A small section of broken-down food is taken up by decomposers and is immobilised by them

• Leaching: the catabolised and fragmented particles contain a lot of water-soluble nutrients that are inorganic. These nutrients are subjected to get dissolved in water by percolating deep into the soil and thus get precipitated in the process of leaching

• Humification: it leads to the accumulation of a dark coloured amorphous substance known as humus, which is rich in lignin and cellulose. It undergoes decomposition at a slow rate and is highly resistant to microbial action. Humus is generally colloidal. It also acts as a reservoir of nutrients and is helpful in the maintenance of soil moisture and aeration 

• Mineralisation: humus further gets degraded by some other microbes and releases inorganic nutrients that occur via the process of mineralisation. It involves both non-minerals and minerals from organic matter. It is a slow process as it involves trapping in of humus and immobilisation in decomposers

• Aerobiosis: activity of decomposer organisms are better in presence of aerobic conditions because decomposition in oxygen is a requiring process. Whereas anaerobiosis leads to piling up of detritus and it also reduces the rate of decomposition

Factors Affecting Decomposition

The three factors affecting decomposition are:

• Temperature: it helps in the regulation of growth and activities of microorganisms. At cold places, the rate of decomposition is slow, as compared to warmer places where the rate of decomposition is quick

• Moisture: dry areas have a slow rate of decomposition, whereas places that have moisture increase the rate of decomposition. Since water is present in the soil that is responsible for conducting various physiological processes of microorganisms present in the soil

• pH: a soil pH is an indication of acidic soil, and this type of soil helps in the decomposition of organic matter. Thus, the rate of decomposition is quick, if the soil has less pH i.e. the soil is acidic than at high pH when the soil is alkaline or basic

Conclusion

 A healthy ecosystem provides a wide range of economic, environmental, and aesthetic goods and services. The products of an ecosystem are known as ecosystem services, this includes a healthy forest ecosystem that helps in purifying air, and water provides wildlife habitats, maintains biodiversity, pollinates crops, etc. Therefore, we must conserve our ecosystem.